Sleep and circadian rhythm disturbances are common features of bipolar disorder. Childhood onset bipolar disorder (COBD), in particular, is characterized by symptoms suggestive of altered regulation of sleep and wakefulness. An associated clinical observation is that children with bipolar disorder exhibit problems with heat dissipation. Despite the pervasiveness of parental complaints and frequent clinical observations of these issues, there are few studies of sleep and rest/activity patterns in COBD, and data relating to body temperature in COBD are virtually non-existent. It is likely that methodological complexities of obtaining such data in children with psychiatric disorders is a primary reason for the lack of studies of this nature. In addition, the very concept of early onset bipolar disorder has been controversial, and only in the last decade have empirical investigations targeting this population been conducted. Recent findings support the classification of COBD as a condition that shares many similarities with, yet is different in important ways, from adult onset bipolar disorder, and other childhood psychiatric disturbances. The aim of this R21 proposal is to evaluate whether nocturnal sleep, circadian and ultradian activity patterns, and thermoregulatory measures differ between children with bipolar disorder (who exhibit manic and psychotic symptoms) and healthy young controls. The study will take advantage of novel, non-invasive technology that enhances the feasibility of assessing sleep and rhythm parameters in children by using actigraphy and wireless temperature monitoring in a home-based study. We hypothesize that compared with controls, children with bipolar disorder will exhibit a phase delay of circadian activity and melatonin rhythms, a consistent ultradian pattern of morning hypoactivity and evening hyperactivity that manifests as enhanced amplitude of the daily activity rhythm, plus longer sleep onset latency and reduced sleep continuity. In addition, the skin temperature gradient measured before and following nocturnal sleep will differ in bipolar children relative to controls, providing evidence of altered heat dissipation. This exploratory project is viewed as an important step toward enhancing our understanding of the biological and physiological factors underlying COBD, and may provide empirical evidence of altered thermoregulatory and circadian regulation of sleep and wakefulness in children with the disorder. In doing so, it has the potential to inform intervention studies or identify novel treatment avenues for COBD, such as therapeutic cooling, exogenous melatonin administration, or timed light therapy. PUBLIC HEALTH RELEVANCE Children with bipolar disorder experience severe social, cognitive, and developmental consequences. The proposed exploratory study will assess sleep, circadian activity patterns, and temperature in this population with the aim of confirming the presence and severity of clinically observed and parent- reported sleep disturbance. The study will shed light on the etiology and biological underpinnings of the disorder, with the ultimate aim of identifying novel and effective treatment approaches for managing the sleep problems that contribute to the burden of bipolar disorder on both patients and their families.